Schistosomin, a peptide present in the haemolymph of Lymnaea stagnalis infected with Trichobilharzia ocellata, is produced only in the snail's central nervous system

A peptide, schistosomin, is present in haemolymph of Lymnaea stagnalis infected with Trichobilharzia ocellata. There are indications that schistosomin is produced by the central nervous system (CNS) of the snail. Schistomin inhibits the effects of the snail's gonadotropic hormones, e.g. calfluxin (CaFl). CaFl stimulates Ca²⁺ influx into the mitochondria of the albumen gland, as shown using the ultracytochemical potassium pyroantimonate precipitation technique. We investigated the question as to whether schistosomin is produced only by the snail or by both the snail and the parasite. Several types of extract of stages of the parasite and of the CNS of the snail were tested for their capability to inhibit the CaFl response. Acid extracts of cercariae and of CNS showed an inhibitory effect, suggesting that both contain schistosomin. From these extracts, material was obtained that showed the same HPLC characteristics as schistosomin. This material was tested again. The hormone response was inhibited only by material derived from the CNS of the snail, indicating that the parasite does not produce schistosomin.